Compression ignition engines provide advantages in fuel economy, but produce both NOx and particulates during normal operation. New and existing regulations continually challenge manufacturers to achieve good fuel economy and reduce the particulates and NOx emissions. Lean-burn engines achieve the fuel economy objective, but the high concentrations of oxygen in the exhaust of these engines yields significantly high concentrations of NOx as well. Accordingly, the use of NOx reducing exhaust treatment schemes is being employed in a growing number of systems.
One such system is the direct addition of ammonia gas to the exhaust stream. It is an advantage to deliver ammonia directly in the form of a gas, both for simplicity of the flow control system and for efficient mixing of reducing agent, ammonia, with the exhaust gas. The direct use of ammonia also eliminates potential difficulties related to blocking of the dosing system, which are cause by precipitation or impurities, e.g., in a liquid-based urea solution. In addition, an aqueous urea solution cannot be dosed at a low engine load since the temperature of the exhaust line would be too low for complete conversion of urea to ammonia (and CO2).
Due to its caustic nature, transporting ammonia as a pressurized liquid can be hazardous if the container bursts, as the result of an accident, or if a valve or tube breaks. In the case of using a solid storage medium, the safety issues are much less critical since a small amount of heat is required to release the ammonia and the equilibrium pressure at room temperature can be—if a proper solid material is chosen—well below 1 bar. Solid ammonia can be provided in the form of disks or balls loaded into a cartridge or canister. The canisters are then loaded into a mantle or other storage device and secured to the vehicle for use. Appropriate heat is applied to the canisters, which then causes the ammonia-containing solid storage material to release ammonia gas into the exhaust system of a vehicle, for example.
However, eventually the ammonia in a canister is depleted and must be recharged or replaced. Unfortunately, there are no systems in place which indicate the fill-status of a canister. This short-coming requires a number of canisters to be used in a system to provide redundancy, and the canisters are typically changed on a regular basis to avoid the possibility of depletion during engine operation. The result is sometimes the carrying of an insufficient amount of ammonia to provide the desired redundancy, and sometimes the removal and replacement of partially-filled ammonia canisters with full canisters to avoid depletion. Such conditions and procedures may increase the possibility of an accidental ammonia release.
Thus, the present system and methods provide for fill-status indication on-board vehicles and on individual canisters. The system and methods facilitate proper scheduling of removal and replacement of ammonia canisters as well as providing real-time ammonia loads for canisters. These and other problems are addressed and resolved by the disclosed systems and method of the present application.